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Discussion Starter #1
Hello again!

I posted recently on a delay when engaging reverse in my 79 Silver Shadow 2. I suspect the cause of the slippage may be hardened seals and that a transmission seal renewal is on the horizon, but getting the transmission out will require some planning. In the meantime I was advised that I may buy some time by using an additive such as K&W Trans-X.

What advice do the experts here have regarding the benefits/disadvantages of transmission fluid additives and what additives if any would you recommend for this purpose in this car (preferably available in the UK)?

Thanks.
Peter
 

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Have you properly checked the level? Trans are big hydraulic pumps that require clean fluid to work. You may also have a dirty filter, worn bands, etc. The TH400 is a very robust transmission.
 

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Discussion Starter #3
Thanks Wraithman, that's encouraging.

I will change the filter and sump gasket first. The fluid colour is not too bad and doesn't smell burnt. If I understand correctly I can only change about half the fluid by draining it through the sump drain hole because the rest is in the torque converter.
 

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Hi,


I have always considered most aftermarket additives as 'snake oil'.


That said I do add ZDDP to my oil on some cars I have since the oil manuafcturers have drastically reduced or elimiated it..............no oil wars............:devil


Also at Jaguar, especially on the old XJS we used to suffer diff whine on the GKN transmission axle. It was not every car, probably 1 in 500 and despite detailed teardowns and individual part by part inspections no one could ever find out the root cause.


The manager who was the specialist used to come with a small container of liquid about the size of a table salt condiment. Once that was added the whine disappeared. I asked why don't you just put it in every car........after a tribology lecture and the fact the tiny little bottle of what he had cost around £30, he said we only do it when there is a problem.


So additives can work I suppose is the answer. That said do the usual checks as wraithman says and if all fails then it appears you have nothing to lose so worth a try and if something does show a result let us know.


Steve
 

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"if all fails then it appears you have nothing to lose so worth a try and if something does show a result let us know."

I will certainly do that.

Peter
 

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Peter, have you ever replaced a transmission filter? You may want to check the level first, it may need fluid. Question, do you know how to check it?
If not, we can help.
 

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Discussion Starter #7
Hi Wraithman

No to filter replacement, and sort of to checking the level (learned by an error):

Actually I checked the level cold and it was below the tip of the dipstick so I topped it up to halfway from the tip to the minimum, then drove it for a couple of miles which blew tx fluid up the dipstick (oddly enough my wife's new name for me!) and made lots of white smoke as it hit the exhaust manifold.

Bottom line is I did learn how not to do it!

Any advice very welcome.
 

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Better than oil additive , use a premium quality oil, such as Dexron III (H) for your car.
High quality oil do not need additive because they have some yet. Adding others may have wrong effect and some unwanted consequences.


Oil level : never cold, but hot after driving minimum 20 km,with engine iddling on park


You should check again, you may have too much oil which is very bad.


Good idea in any case to drain oil and clean filter. If oil is dirty and smell, you may have ta change it 2 or 3 times
 

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Discussion Starter #9
Thanks Jean7.

I have read that too much oil is very bad but apart from frothing and overspilling, why is it so damaging?
 

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Hi,


Totally out of my area the mechanics of engines, gearboxes and Diffs.:devil


Have you thought though could it be a bad electrical contact, the connection at the gearbox can often get contaminated.


Also could it be some linkages needing a bit of oiling.


That's about all my input and 2p's worth so back to the mechanics advice of others.


All the best


Steve
 

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The only electrical connection, other than the actuator harness, which apparently works, is a 2 blade connector on the same side of the gearbox for the "downshift" solenoid". On later cars there would be a 3rd connection due to the changeover from mechanical to electrical on the speedo drive.

It seems to me this issue if fluid/maintenance-related.

It can be a real mess for a beginner to tackle and a knowledge of filter install, checking fluid level, proper pan bolt tightening pattern/torque.

Any shop with GM experience can handle this. It's a great transmission, so good RR used it.
 

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I suppose pressure inside the trnasmission. Mercedes specialist warned me several time, better not nough than too much. Too much is really the worst.
 

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It will usually come out of the small vent tube on top of the transmission case and or the filing tube in the engine bay.
 

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James,
The internal seals of your 1979 transmission are hardened. They don't owe you nothing no more. Your transmission needs to be pulled and overhauled. It's not that complicated, the TH400 is very, very collaborative for working on it. You'll love the way your car drives thereafter.
 

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Most of the important seals can be done in situ. Piston, front pump, etc.
 

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Not even half of the seals can be done in situ. Certainly not the front pump seals.
Only the pan gasket seal, the kick down solenoid, tachometer and flywheel seal and the filter seals (obviously) can be done in situ, and furthermore the valve body seals, front and rear accumulator seals.
Attached a pic of a typical TH400 seal kit, encircled in magenta are the ones that are replaceable in situ.
If an accumulator seal (reachable in situ) is perished, the piston seal inside the transmission will be perished as well. Guaranteed.
Replacing the seals on the valve body in situ will only make you lose time, as the whole valve body needs to come apart again (and seals need to be replaced again) if you do the internal seals (need to access the center support bolt).
 

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